The disproportionately severe cholinergic deficit in DLB compared to AD is a critical teaching point. It explains (1) why visual hallucinations are so prominent (cholinergic deficit in visual cortex), (2) why attentional fluctuations occur (cholinergic modulation of cortical arousal), and (3) why acetylcholinesterase (AChE) inhibitors work better in DLB than in AD.

Lewy bodies are round, eosinophilic, intracytoplasmic neuronal inclusions composed of phosphorylated alpha-synuclein ^[2][4]. Let's break this down:

1. Normal α-synuclein: A small (140-amino-acid) presynaptic protein involved in synaptic vesicle trafficking, neurotransmitter release, and synaptic plasticity. It is normally unfolded ("natively unfolded") in solution.

2. Misfolding: Under pathological conditions (oxidative stress, ageing, genetic predisposition), α-synuclein adopts an abnormal β-sheet-rich conformation → this makes it prone to aggregation.

3. Oligomers → Fibrils → Lewy bodies: Misfolded α-synuclein first forms toxic soluble oligomers (which are the most neurotoxic species), then insoluble fibrils, which accumulate as:

   • Lewy bodies: Dense, round inclusions with a halo
   • Lewy neurites: Thread-like aggregates in neuronal processes

4. Prion-like spreading: α-Synuclein aggregates can spread cell-to-cell in a prion-like manner — this explains the progressive, stereotyped anatomical spread of pathology (brainstem → limbic → neocortical).

5. Mechanisms of neurotoxicity:

   • Mitochondrial dysfunction (α-synuclein oligomers inhibit Complex I)
   • Endoplasmic reticulum stress and impaired protein degradation (proteasomal and lysosomal)
   • Synaptic dysfunction and neurotransmitter release impairment
   • Neuroinflammation (microglial activation)

Alzheimer disease copathology is observed in at least 50% of individuals with DLB ^[3]. This is a crucial point:

• Amyloid-beta (Aβ) plaques and neurofibrillary tangles (tau) frequently coexist with Lewy body pathology
• Copathology is clinically associated with greater cognitive decline, greater risk of institutionalisation, and mortality ^[3]
• Other copathologies: TDP-43, cerebrovascular changes
• This explains why some DLB patients present with amnestic features (more typical of AD) alongside the characteristic DLB features

Three prodromal DLB syndromes have been proposed ^[3]:

(Core features, indicative biomarkers, and supportive features will be expanded in the Diagnosis section — here we focus on clinical features.)

Dementia in DLB is characterised by early impairments in attention, executive function, and visuospatial function (memory is affected late) ^[2][4]

Key Contrast with AD: In AD, the earliest and most prominent deficit is episodic memory (hippocampal encoding failure — information never gets stored, so cueing doesn't help). In DLB, memory is a retrieval problem (information is stored but hard to access — cueing helps). DLB patients show much more prominent attentional and visuospatial deficits than AD patients at equivalent disease stages.

These features support the diagnosis but are not core criteria:

Autonomic dysfunction in DLB is more severe and earlier than in typical AD, because α-synuclein deposits in peripheral autonomic ganglia and brainstem autonomic centres:

1. Onset and tempo: Insidious onset, progressive course (unlike delirium which is acute, or VaD which may be stepwise)
2. Cognitive profile: Ask about navigation difficulties (visuospatial), planning/multitasking (executive), concentration (attention)
3. Fluctuations: "Does [patient] have good days and bad days in terms of alertness?" "Do they blank out or stare into space?"
4. Hallucinations: "Does [patient] see things that aren't there? Can they describe what they see?" (Well-formed, detailed descriptions are characteristic)
5. Sleep: Ask bed partner about dream-enacting behaviours — this is often the earliest clue
6. Motor: "Has [patient] become slower? More stooped? Shuffling feet? Any tremor?"
7. Falls: "How many falls in the last 6–12 months?"
8. Autonomic: Dizziness on standing, constipation, urinary symptoms
9. Drug history: Any previous antipsychotic reactions? This is critical.
10. Psychiatric: Mood, anxiety, delusions
11. Timing: Establish whether cognitive decline came before or within 1 year of any motor symptoms (→ DLB vs PDD)

• Cognitive assessment: MMSE, MoCA (MoCA is more sensitive for executive/visuospatial deficits seen in DLB)
• Neurological exam: Full extrapyramidal assessment (tone, bradykinesia, tremor, gait, pull test)
• Lying and standing BP (orthostatic hypotension)
• General appearance: Hypomimia, drooling, stooped posture
• General awareness and alertness: fluctuations may be observed during the interview ^[6]

This is the single most important differential because DLB and PDD share identical pathology (cortical Lewy bodies).

D/dx: PD-dementia — differentiation arbitrary; generally dementia occurs in well-established Parkinsonism in PDD, whereas dementia occurs with or before Parkinsonism in DLB ^[2][4]

The 1-year rule remains in effect to clinically differentiate DLB from PDD: if dementia occurs before or within 1 year of motor symptoms of bradykinesia, rigidity, or resting tremor, a diagnosis of DLB is established ^[3]. If dementia develops after 1 year of the onset of motor symptoms or an established diagnosis of PD, then the diagnosis of PDD is given ^[3].

Why does this distinction matter clinically? Although the pathology is the same, the distinction has prognostic and management implications. DLB patients tend to have a more aggressive course with earlier neuropsychiatric features and greater antipsychotic sensitivity risk, while PDD patients have had years of motor management before cognitive decline begins. DLB and PDD are both synucleinopathies with two different phenotypes with a shared underlying pathology ^[3].

AD is the most common misdiagnosis given to DLB patients. The key differentiators:

Why the overlap occurs: Copathology with Alzheimer disease occurs in more than 50% of patients with DLB. Individuals with this mix of pathology experience more memory changes and faster disease progression ^[3]. So a patient with DLB + AD copathology may present with prominent memory impairment (atypical for "pure" DLB), making the differentiation extremely difficult without biomarkers.

Dementia with Lewy bodies is more commonly confused with delirium as fluctuations and visual hallucinations are more prominent ^[7]

This is a critical differential, especially in the hospital setting. Both DLB and delirium share:

• Fluctuating attention and awareness
• Visual hallucinations
• Altered sleep-wake cycle
• Psychomotor disturbance

Fluctuations can occur in non-DLB delirium; therefore, fluctuations are not specific to DLB ^[3]. Visual hallucinations can also occur in non-DLB delirium and can be drug-induced or related to substance withdrawal ^[3].

Key clinical pearls:

• Dementia with Lewy bodies patients are extremely vulnerable to delirium — delirium occurs more frequently in those later diagnosed with DLB compared to AD (25% vs 7%) ^[3]
• Delirium should be ruled out if there is any change in pattern of fluctuation from baseline ^[4]
• Suspect delirium-onset DLB when: provoking factors not identified, prolonged or recurrent delirium, subsequent progressive cognitive decline ^[3]

Fluctuations — delirium, dementia with Lewy bodies ^[6]. Both conditions should be considered when fluctuating awareness and alertness are observed.

Why the confusion may arise: Both FTD and DLB can present with executive dysfunction, behavioural change, and apathy. However, the presence of RBD, visual hallucinations, cognitive fluctuations, and parkinsonism strongly favours DLB. Conversely, prominent disinhibition, loss of social conduct, hyperorality, and stereotyped behaviour favour bvFTD.

Early and prominent movement disorder suggestive of dementia with Lewy bodies or other α-synucleinopathy or other nonvascular movement disorder is a feature that may suggest an alternative predominant aetiology to vascular disease ^[10].

Practical note: Cerebrovascular copathology is common in DLB (as in most elderly dementias). The question is whether the vascular burden is sufficient to explain the cognitive syndrome, or whether it is incidental. If core DLB features are present, they should not be attributed to VaD even in the presence of vascular lesions.

D/dx: NPH — no psychiatric symptoms, sleep disorder, or dysautonomic features ^[2][4]

Why this matters: NPH is one of the few treatable/reversible causes of dementia. Missing NPH in favour of a DLB diagnosis means missing a potentially curable condition. Conversely, misdiagnosing DLB as NPH (because both have gait disturbance and cognitive decline) could lead to unnecessary VP shunting. The absence of psychiatric symptoms, sleep disorder, and dysautonomic features in NPH helps distinguish the two ^[2][4].

Red flags of atypical Parkinsonism include: early falls / postural instability, early dementia, bilateral symmetrical onset, early ANS dysfunction, poor response to L-DOPA ^[1]. Several of these overlap with DLB, making differentiation challenging:

Key teaching point: Both DLB and these Parkinson-plus syndromes are causes of atypical parkinsonism with poor response to levodopa. The differentiators are the specific non-motor features:

• DLB = VH + fluctuations + RBD + early dementia
• MSA = dysautonomia + cerebellar signs + no early dementia
• PSP = vertical gaze palsy + axial rigidity + falls backward
• CBD = asymmetric apraxia + alien limb

This differential is particularly relevant for psychiatric-onset DLB.

It is vital to recognise the psychiatric-onset prodromal DLB syndrome given the risk of severe antipsychotic sensitivity among individuals with DLB, which is associated with increased morbidity and mortality ^[3].

An important practical differential in any elderly patient with parkinsonism:

• Causative agents: Metoclopramide, antipsychotics (typical > atypical), antihistamines ^[11]
• Key features: Bilateral, symmetric parkinsonism (similar to DLB); temporal relationship to drug initiation
• Differentiation: Drug-induced parkinsonism should resolve on withdrawal of the offending agent (may take weeks to months). DAT-SPECT is normal in drug-induced parkinsonism (because nigrostriatal neurons are intact — the drug is blocking the postsynaptic D2 receptor, not destroying presynaptic neurons)
• Trap: If a DLB patient receives an antipsychotic and develops severe parkinsonism, this could be misinterpreted as drug-induced parkinsonism when it is actually antipsychotic sensitivity in the context of underlying DLB ^[2]

Non-convulsive status epilepticus requires EEG for detection ^[7][4]

• May present with fluctuating consciousness, confusion, and behavioural change — mimicking both delirium and DLB
• Clues: Subtle motor phenomena (facial twitching, nystagmoid eye movements, automatisms like lip smacking)
• Diagnosis: EEG showing continuous or near-continuous epileptiform discharges
• Important because: It is a treatable cause of fluctuating confusion that should not be missed

When to think CJD: Any rapidly progressive dementia (weeks–months, not years) with myoclonus should raise red flags for CJD. The tempo alone usually distinguishes it from DLB.

Progressive cognitive decline of sufficient magnitude to interfere with normal social or occupational function ^[3]

• This is the definition of dementia per DSM-5: decline from a previous level of performance in ≥ 1 cognitive domain that interferes with independence in everyday activities ^[2]
• Prominent and early deficits in attention, executive function, and visuoperceptual processing ^[3]
• Memory impairment may not be prominent in early stages but usually develops with progression

Core clinical features ^[3][4]:

Supportive clinical features ^[3][4]:

• Severe sensitivity to antipsychotics
• Hypersomnia
• Postural instability
• Hyposmia
• Repeated falls
• Hallucinations in other modalities
• Syncope or other transient episodes of unresponsiveness
• Systematized delusions
• Severe autonomic dysfunction
• Apathy, anxiety, and depression

Supportive features increase diagnostic confidence but do not count towards the "core feature tally" used for probable vs possible classification.

Indicative biomarkers ^[3]:

Supportive biomarkers ^[3]:

Probable DLB ^[3]:

Two or more core clinical features, OR one core clinical feature plus one or more indicative biomarkers

Possible DLB ^[3]:

One core clinical feature only (no indicative biomarker), OR one or more indicative biomarkers only (no core clinical features)

Logic of the system: The classification is designed to be hierarchical. Core clinical features carry the most diagnostic weight because they are the clinical hallmarks of Lewy body pathology. Indicative biomarkers can "substitute" for a missing core feature because they provide objective evidence of the underlying pathology (dopaminergic degeneration, autonomic denervation, or REM sleep dysregulation). Supportive biomarkers and supportive clinical features increase confidence but cannot substitute for core features.

Research criteria for MCI due to Lewy bodies ^[3]:

Neuropsychological testing should be pursued ^[3] with a battery assessing:

• Executive function and attention: trail-making tests, Stroop task, phonemic fluency test, Wisconsin Card Sorting Test ^[3]
• Visuospatial: figure copy tasks (intersecting pentagons, complex figures), line orientation, size matching, fragmented letters test, and the pareidolia test ^[3]

The pareidolia test is a tool that evokes and measures visual hallucination-like illusions of meaningful objects from ambiguous visual scenes ^[3]. This is uniquely useful in DLB because patients with posterior cortical dysfunction "see" meaningful images in random patterns at much higher rates than AD or healthy controls.

Because fluctuations are subjective and can be difficult to quantify:

• Clinician Assessment of Fluctuation (CAF): clinician rates the severity and frequency of fluctuating episodes
• One Day Fluctuation Assessment Scale (ODFAS): carer-completed questionnaire documenting cognitive variability over 24 hours
• Clinical Dementia Rating (CDR): general dementia severity scale; in DLB, there may be discrepancy between performance on "good" vs "bad" days

• Purpose: Objective confirmation of REM sleep behaviour disorder (RBD)
• Key finding: REM sleep without atonia (RSWA) confirmed on polysomnography ^[3] — electromyographic activity during REM sleep that is normally absent
• Clinical correlation: Converts the clinical history of "dream enactment behaviour" (which is a core clinical feature) into a confirmed biomarker (which is an indicative biomarker)
• Interpretation: RSWA on PSG + 1 other core feature → probable DLB

Why this matters: Bed-partner history of RBD counts as a core clinical feature, but PSG-confirmed RSWA counts as an indicative biomarker. This means PSG confirmation can "upgrade" a diagnosis from possible to probable DLB in the right clinical context.

EEG: posterior slow-wave activity with periodic fluctuations in the pre-alpha and pre-theta range ^[3]

Why it helps: The combination of posterior slowing plus periodic fluctuations has good sensitivity for DLB and helps differentiate from AD (where EEG is usually normal or shows less specific changes early on). EEG also excludes non-convulsive status epilepticus (NCSE) — a critical differential that requires EEG for detection.

Given that AD copathology is observed in at least 50% of individuals with DLB ^[3], assessing for coexisting AD pathology is clinically relevant:

Clinical significance: Positive AD biomarkers in a DLB patient indicate mixed pathology. These patients tend to have greater cognitive decline, greater risk of institutionalisation, and mortality ^[3]. This also explains why some DLB patients present with prominent memory impairment — the amnestic component is driven by the coexisting AD pathology.

Every dementia workup must include screening for reversible causes (which account for 10–15% of dementia presentations) ^[2]:

This is the first and most important step in DLB management. Many commonly prescribed medications can dramatically worsen DLB symptoms.

A comprehensive medication review should be conducted at each evaluation to ensure the person with LBD is not taking medications or over-the-counter drugs that may worsen their cognition or trigger psychosis ^[3]

Avoid the use or minimise the use of antipsychotics and anticholinergic medications in individuals suspected of having delirium-onset DLB ^[3]. Avoid the use or minimise the use of antipsychotics and anticholinergic medications in individuals suspected of having psychiatric-onset DLB ^[3].

DLB progresses faster than Alzheimer disease ^[3]:

• Survival approximately 5–8 years from symptom onset ^[3]
• Average lifespan 7.7 years ^[4]
• Most common cause of death: failure to thrive (65%), pneumonia and swallowing difficulties (23%), other medical conditions (19%), complications from a fall (10%) ^[3]
• Copathology with AD accelerates decline
• Factors associated with worse prognosis: older age at onset, AD copathology, more severe autonomic dysfunction, early institutionalisation

• Prevalence: Depression in ~30–50% of DLB patients; anxiety in ~25–50%
• Mechanism: Degeneration of serotonergic (dorsal raphe nuclei) and noradrenergic (locus coeruleus) systems → monoamine depletion in limbic circuits
• Impact: Depression in DLB worsens cognitive function, accelerates functional decline, increases caregiver burden, and is associated with higher mortality
• Complication of depression: Suicidal ideation — patients with preserved insight (early disease) who understand their progressive diagnosis are at risk

• Visual hallucinations are a core feature, but they can progress from benign (patient has insight, not distressed) to severe and distressing (loss of insight, fear, agitation)
• Systematised delusions (persecutory, Capgras syndrome — believing a loved one has been replaced by an impostor) can cause behavioural disturbance and relationship breakdown with caregivers
• Complication: Agitation, aggression, resistance to care → risk of self-harm or harm to caregivers → inappropriate use of restraints or antipsychotics (which creates the neuroleptic sensitivity complication above — a vicious cycle)

• Not simply "depression without sadness" — it is a distinct syndrome involving loss of motivation, initiative, and emotional engagement
• Driven by mesocortical dopaminergic and cingulate cortex dysfunction
• One of the most distressing symptoms for caregivers because the patient appears indifferent to everything

• Patients physically act out violent dreams → self-injury (falling out of bed, hitting furniture) or bed partner injury (punching, kicking, choking)
• This can result in significant trauma including lacerations, bruising, and fractures
• May lead to bed partner sleeping separately → social isolation → worsening depression

• Due to disruption of brainstem arousal centres (locus coeruleus, pedunculopontine nucleus)
• Hypersomnia is a supportive clinical feature ^[2][4]
• Consequences: Falls (falling asleep in chairs, during activities), impaired engagement with rehabilitation, reduced quality of life, increased caregiver burden